How long does a prep course take?

Prep classes last any where from a week to several months. I think the one week courses are too short because the kids get barraged with too much information in a short period of time. A class that is 4 to 5 months long can get to be a grind for most kids. In my experience, 5-8 week courses are best because they give kids time to digest what they learn without becoming a grind.